There is known a device for introducing samples into an analyzer of an apparatus for granulometric analysis of particles contained in fluids, comprising a vertical cone-shaped funnel and a straight vertical channel which communicates the outlet of the funnel with a supply channel of an analyzer.
A sample of a fluid to be subjected to analysis is poured into the funnel and flows through the vertical channel to the supply channel of the analyzer where particles of impurities are analyzed.
The pouring of fluid into the funnel is usually accompanied by the formation of air bubbles which may reach the analyzer with the flow of fluid and be mistaken for particles of impurities.
The result is a reduced accuracy of the analysis because the number of particles detected by the apparatus is greater than their actual quantity. To eliminate the air bubbles, the sample must either be evacuated or allowed to settle so that the air bubbles should be driven out by the buoyancy forces; in the latter case it is necessary to close the discharge cock. The settling time is dependent on the size of the bubbles, as well as on the viscosity and density of the fluid. However, as air bubbles are removed in the course of settling, particles of impurities precipitate under gravity. Some of these particles precipitate on the walls of the funnel, whereas others reach the vertical channel and get as far as the supply channel of the analyzer. If a stopcock is installed at the analyzer's inlet, particles precipitate on the submerged part of the stopcock; when the latter is opened these are washed away by the flow and carried to the analyzer for the most part in the form of large aggregates. As a result, the apparatus detects particles in a number smaller than that contained in the sample, and of a size greater than that of particles originally contained in the sample. Besides, the friction parts of stopcocks, as a rule, also produce impurities, which accounts for considerable errors in determining the amount of impurities contained in fluids.
The latter disadvantage is eliminated by installing and closing a stopcock at the outlet of the analyzer. However, in such a case some of the precipitated particles pass through the analyzer which is out of operation, keeping in mind that it is designed to determine the amount and size of particles in a flow of fluid. As the analysis begins, the particles passed through the analyzer are not taken into account, wherefore the apparatus detects a lesser quantity of particles than that actually contained in the sample.